It's a bad compromise. If you want the cheapest transfers, you batch them. (This is the logic of Lightning.) If you want the most reliable transfer, you wire it. If you want to be sneaky, you use cash. (There are other reasons to use these modes.)

Batching being cheaper and slower than RTGS is fundamental to payment economics, irrespective of whether in an electronic database, armored car or blockchain. I go into this in a comment from about a year ago [1].

[1] https://news.ycombinator.com/item?id=16154956#16155708